The present invention relates generally to mobile communication systems, and more particularly, to a highly compressed voice and data transmission or communication system and method that may be used for mobile communications.
In most mobile communications systems it is necessary to use low frequency radio waves in order to achieve building penetration and to achieve practical omnidirectional antenna systems. At low frequencies, there is limited bandwidth that is available. Furthermore the bandwidth that is available is also typically used for other applications. For these reasons it is necessary to use the available spectrum (bandwidth) as efficiently as possible. To date, a digital voice compression ratio of about 10 to 1 is about the best that has been achieved with acceptable quality. This requires transmission data rates of approximately 5 kbps and bandwidths of approximately the same numerical value in kHz.
It would therefore be desirable to have an improved voice and data transmission or communication system and method that highly compresses voice and data signals to improve the use of the limited available frequency bandwidth, and to overcome limitations of conventional approaches. Accordingly, it is an objective of the present invention to provide for a voice and data transmission or communication system and method that compresses data to provide for an improved low frequency mobile communications system.
To accomplish the above and other objectives, the present invention provides for a communication system and method that compresses voice and data signals by at least an order of magnitude compared to the 10:1 conventional data compression ratio. The present system and method combines the use of several currently available technologies to achieve this dramatic improvement in compression. The large compression ratio achieved by the present invention permits greater use of the limited bandwidth at the low frequency of operation of the communication system.
An exemplary system comprises a voice recognition system that converts spoken words into a sequence of letters and gaps. An encoder is used to code the letters into a digital message. A transmitter is used to transmit the digital message to a receiver over a mobile communications link (such as a cellular communications network). The receiver is used to decode the digital message and a speech synthesizer is used to convert the decoded message into spoken words.
The system is symmetrical so that a normal voice conversation may take place between two individuals. Each individual uses a device containing the voice recognition system, encoder, transmitter, receiver and speech synthesizer. Each device is coupled to a microphone and a speaker, such as those used in a normal telephone system, to serve as an interface to a human ear and voice, respectively.
The system may optionally use a special function that causes the speech synthesizer to more accurately resemble a speaker""s voice. This is accomplished by transmitting an initial message that identifies one of a plurality of stored voice types that is to be synthesized, or by sending a simultaneous signal that tailors the voice synthesizer in real time as the voice of the speaker changes.
The system may also optionally use a visual display for displaying the message at the receiver for hearing impaired users and users located in noisy areas. This may be implemented using a speech-to-text processor coupled to a display. This feature may also be used to transmit messages to a digital storage device coupled to the decoder, for example.
The system may also optionally use a digital interface to the transmitter so that nonspeaking individuals may communicate with a key pad or other device that is used to generate the message to be transmitted. This feature may also be used for transmitting stored files to the receiver for use at the receiving end of the system.
In an exemplary method, words are spoken into a microphone by an individual that are to be transmitted to an second individual. The spoken words are converted into a sequence of letters and gaps using a voice recognition system. The sequence of letters is then coded into a digital message. The digital message is then transmitted to a receiver over a mobile communications link. The digital message is decoded at the receiver. The decoded digital message is converted into spoken words using a speech synthesizer. The converted into spoken are then broadcast using a speaker so that the receiving individual can hear what was spoken at the other end of the communication link.
The system and method are symmetrical so that a normal voice conversation may take place between two individuals each using a device containing a transmitter and a receiver. This device is coupled to a microphone and a speaker of a normal telephone system to serve as an interface to a human ear and voice, respectively.